Regulatory interactions between metabolic pathways has been well documented and may function to maintain the optimal levels of essential cellular metabolites. Allosteric effectors serve as appropriate signals in mediating interpathway regulation, and there is evidence that a protein which functions as a subunit in two or more enzyme complexes from distinct biochemical sequences may serve a similar role. One such protein has been found and described in Bacillus subtilis. In this system, the common protein is subunit X, the product of the trpX locus, which functions as a glutamine binding potein in the following manner. (1) Subunit E, the product of the trpE locus, catalyzes the formation of anthranilic acid (O-aminobenzoic acid) with ammonia as a substrate. Although this protein cannot utilize glutamine, an EX complex can catalyze the transfer of the amide group from glutamine to form anthranilate. (2) Subunit A, the product of the pabA locus, is anaogous to subunit E except that the product is p-aminobenzoic acid (PABA is an essential moiety of folic acid) and subunit X forms a complex with subunit A to constitute an amidotransferase. Subunit X alone cannot form anthranilate or PABA. This interesting relationship is the subject of this research proposal, and the following overall objectives have been formulated: (1) determine the physiological regulation of subunit X; (2) determine if subunit X functions as a common subunit for other amidotransferases. The general approaches to reach these objectives are: (1) determine the effect of subunit E on the level of subunit X; examine the response of subunit X to regulatory mutations that affect the biosynthesis of tryptophan; (2) isolate mutants by UV or chemical mutagenesis that would have multiple requirements as a result of losing a general glutamine binding protein; isolate and determine the physiological and biochemical consequences of suppressor mutations that affect subunit X.